The present invention relates to a turbocharger for use in intake system of automotive engines and, more particularly, to an improvement in the construction of bearing support in the turbocharger.
Generally, a turbocharger has a rotor shaft which carries at a turbine rotor at one end thereof, with a compressor rotor at the other end thereof. The rotor shaft is supported by radial bearings for bearing the radial load and a thrust bearing for bearing thrust load acting on the rotor shaft. Various types of bearings for bearing radial load have been proposed in which most popular is a floating bush type bearing such as that disclosed in U.S. Pat. No. 3,565,497, with the proposed floating bush type bearing has floating bushes rotatably disposed between the rotor shaft and the bearing housing.
Turbochargers are mass-produced in various sizes to match the capacities of various engines. From a view point of mass-production, it is preferred that these turbochargers of various sizes use a common housing of the same size and shape. However, the size of the turbine section having the turbine rotor and the size of the compressor section having the compressor rotor, as well as the operation speed of the turbocharger, vary depending on the capacity of the turbocharger. As a natural result, turbochargers having different capacities have a different span between bearings. For these reasons, it has been impossible to use a common housing for turbochargers having different capacities.
Another problem arises from the wear of the inner and outer peripheral surfaces of the floating bushes and wear of the inner peripheral surface of a bearing housing which embraces the outer peripheral surfaces of the floating bushes. The wear of the sliding parts of floating bushes and bearing housing are serious particularly in the turbine side of the turbocharger, because the floating bush and a portion of the bearing housing at this side are subjected to the high temperature of the exhaust gas driving the turbine. There are natural allowable limits in the amounts of wear in these sliding parts, in order to maintain the required performance of the turbocharger and to avoid generation of excessive vibration. If the wear exceeds the allowable limit, it is necessary to replace the worn part such as the floating bushes and the bearing housing, otherwise the performance of the turbocharger may seriously deteriorate. The frequent renewal of the bearing housing, however, is quite inconvenient from the view point of saving and utilization of natural resources.